Plated metal having carbide surface



July 2l, 1936 c. A. MARLIES ET Al. 2,048,276

.PLATED METAL HAVING CARBIDE SURFACE I Filed April 2l, 1932 lilla! 0` fa llllllmalmll:

sla

@swam/Af Arf 57m INVENTOR CHARLES A-. MARLIES Patented July 2l, 19,36

APATENT .o1-*FICE PLATED METAL HAVING CARBIDE SURFACE Charles A. Marlies and George E.V White, New York, N. Y., assignors oi' one-half to Bruno S. Teschncr, New York, N. Y.

Application April 21, 1932, Serial No. 606,736

' s claims (C1. 14s-31) Our present invention relates to the carburizing of plated metallic surfaces," and more particularly to novel methods of producing carbided chromium, or tungsten, surfaces on chromium, or

5' tungsten, plated metals, as well as to the novel products resulting from such methods.

peratures, and corrosion-proof properties of ychromium carbide render it an ideal surfacing 'material for metallic bodies which are subjected to severe temperature conditions, abrasion or chemical action. While chromium has been utilized as a surfacing material for such metallic bodies (as for example steel), a brief considerall'tionv of the comparative physical and' chemical' properties of chromium and chromium carbide readily demonstrates that the latter is superior. Thus, whereas chromium carbide has a hardness on Mohs scale of 8.0 to 8.5, specific gravity of 6.7 4-and melting point ,of 2250 C., chromium has a hardness of 6.0, specific gravity of 7.1 and melting point of 1615 C, Again, whereas chromium oxidizes at high temperatures, and is chemically affected by hydrochloric acid, aqua regia, and sul--v `-phuric acid, chromium carbide is stable at high temperatures, and is unaffected by any of the aforementioned chemical agents.

Now, generally, according to our invention, chromium carbide, as distinct from the element chromium, is employed as a surfacing material for metallic bodies, such as steel, and specifically -such a carbide is produced upon a layer of metallic chromium which hasbeen plated upon the metallic body, it being pointed out that the pres- 'ent invention applies equally well to tungsten plated metallic bodies.

Hence, it may be stated that it is a prime object. of this invention to utilize the existing chromium, or tungsten, plate of a metal body. as steel, for the production of a hard, carbidesurface which is not only capable of protecting the underlying metal from abrasion, corrosion or chemical action, but is formed in an exceedingly uniform layer free from microscopic fissures, the `'uniformity not-being impaired by sudden temperature variations. l

Another important object of this invention to provide chromium, or tungsten, plated steel which possesses a chromium, or tungsten, carbide surface capable of resisting to a greater extent than the uncarburized plate the' action of conn such severe conditions of use as in connection with a great variety of equipment used? in the chemical industries.

Still another object of this invention is to provide a carbided surface on a chromium, or tung- 5 sten, plated metallic body, such as steel or alloys I'he extreme hardness, stability at high temthereof,`which can be heated to a red heat and then quenched, without cracking, distortion, or loss of chemical resistivity.

Another object of our invention is to provide l0 a great variety of methods for producing carbided surfaces on chromium, or tungsten, plated steel, the methods basically involving the treatment of the plated steel, at an elevated temperature, with acarbonaceous substance, the latl5 ter beingl one ,of `agentia including such `widely different materials as molten cyanide baths including, as is well known in the art, other fused salts, asphalt, sawdust, mixtures of sand and calcium carbide, case-hardening mixtures, charcoal, 20 and mixtures of gaseous hydrocarbons, such as vaporized benzol, ethylene, acetylene, natural gas,

or illuminating gas.

Still another object of the present invention is to provide a chromium carbide surface on an 25 electroplate of chromium upon steel which surf face is characterized by having a surface hardness of the Brinell scale of the order of four times as great as that of the chromium plate itself, and of -the order of ten times as great as $0 that of the steel, the surfacebeing produced by carburization of the surface of the plate.

Still other objects of the invention are to improve the utility of chromium, or tungsten, plated metallicv bodies, as steel, by providing various 3 5 methods of carburizing the plated surface, the methods not only being commercially practicable, but reliable in operation.

In the following description modes of putting this invention into practice will be disclosed, but 40 we do not wish to be understood as confining the invention to the specific mode of operation, or

' the ingredients set forth, asmany variations may be introduced, well within the spiritof this invention as dened in the claims succeeding the de-` 45 scription.

In thedrawing,

Fig. 1 shows a photomicrograph of the result of a scratch hardness'tesii-on a steel surface,

Fig. 2 shows asimilar photograph of a similar 50 test on the surface of chromium plated steel,

Fig. 3 shows theresult'of -a similar test on a surface embodying the invention,

' Fig. 4 illustrates a photomicrograph of a section of the specimen shown in Fig. 3.

Referring, now, to the accompanying drawing wherein like reference characters in the different figures designate similar elements, there is shown in Fig. 4 a representation of a photomicrograph of an embodiment of the present invention. VThe figure illustrates a section of a ferrous body- I, such as steel, which is provided with a chromium plate '2, the latter having its exposed surface carburized, as shown at 3. Examination of thissection under the microscope indicated a very uniform carbide coat'of the order of 0.002 mm., in thickness, the chromium plate being of the order of 0.006 mm., in thickness. The bond l between the two coats l2 and 3 is not only'exchromium. One possible vmethod is described hereinafter, the carbide surfaces formed being uniform and extremely ne grained. Not only are the surfaces hard and uniform, resisting to a substantial extent the action of concentrated acids and alkalies, but they can be heated to a red heat and then quenched, without cracking, dis- `tortion, or loss of resistance to chemical action.

Generally; the method employed in producing the novel product Ysliown in Fig. 4 consists in'subjecting the plated surface, at an elevated temperature, to i/e. action of a uid carbonaceous material. 2

Specically, the metallic body, as steel,is rst plated with a metal of a group including chromi- .um and tungsten. electrolyticall'y in` any well known manner. Those skilled in the art are well aware of the technique of chromium plating, for example, and

Y therefore it is not believed necessary to describe the plating details, except to point out that the plating is carried out until the desired thickness of chromium, or, tungsten, is deposited on the acetylene.

steel body, preferably at a temperature' of about 65? C. in order to produce a coat of minimum porosity and minimum content of occluded gas. The chromium plated steel body, when ready for carburization, is placed in a carburizing vessel.

When carburization is to be eiectedby means of gaseous hydrocarbon the vessel utilized should permit ready ingress and egress of these gases.

The temperature of the chamber is maintained at about 800 C., for about twenty minutes as a stream of gaseous hydrocarbon,- such as' illuminating gas with or without the enrichment of benzol vapor or other vaporizedliquid hydrocarbons; ethylene; acetylene; natural gas, is passed over the plated body. Additionally, the vplated.l surface may be freedof occluded gases, prior to the carburization, by heating the plated body in vacuo to 300 C., for about thirty minutes. `This pre-treatment, while not essential, may improve the carbide coating if the plate contains much occluded gas. What is important during the carburization, is` that a continuous stream of .the gaseous hydrocarbon be pased over the plated surface so as to ensure the presence of sufficient It is for this reason that methods affording no continuous supply of gaseous hydroimprovement in surface hardness.

Theplating may be effected The most uniform and satisfactory surfaces are produced by the.use of iluid carburizing agents. 'I'his condition is realized in the gaseous carburizing process just described, or in carburization by means of fused baths containing cyanides, or other carbon-bearingmaterials.

It is also pointed out that carburizatlon in a case-hardening furnace may be employed. In' such a case the plated article may be case-h'ardened in any usual manner well known to those skilled inthe art. The case-hardening mixtures which may be sawdust, wood charcoal, mixtures of silica sand and calcium carbide, molten baths containing cyanides, or combinations of these.

`Carbide surfaces aresecured, when using thel first of said aforementioned methods, which 'resist the sudden temperature changes occurring in quenching, as well as the action of concentrated hydrochloric acid. -Proof of the formation of the chromium carbide ysurface is obtained qualitatively by the change in color, the miscroscopic structure', and the reaction toward concentrated hydrochloric acid; quantitatively by the marked increase in surface hardness over that of the original chromium plate.

Figs. l, 2 and 3 illustrate the results of comparative surface hardness tests on the surfaces of the steel body, the chromium plate and the chromium carbide respectively. Thus, in Fig. l eachdivision of the microscope scale represents 0.0023 mm. 'I 'he shaded area' w represents the scratch made with a diamond point pressed against the surface o f the steel by a known weight. This scratch test is well known to those skilled in the art, and is employed as a measure A of surface hardness of thin metallic coats. The

width of the scratch produced by the diamond point was 0.0097 mm., under a 20 gram load.

'I'he value'S, representing the scratch hardness number, vcan'be shown to be obtainable by the expression:

:gg-g where L--ethe load in kg.

S, for the untreated steel surface, has a number of 550. Fig. 2 shows the width of the scratch prof herein named' methods. The valuev of u is' 0.0023 mm., under the same conditions: while, 8 has been greatly increased to 9600, a magnitude ofthe order of twenty times that of the untreated steel surface and four times that of the lchromium surface. It is to be noted however, that S may have a value (depending on the carburization methodV employed) ranging between six and twenty times as great as that .of -an imtreated steel surface.

The characteristics of the surface shown in Fig. 3 may be denedA as being purple in color,

the range lof 4 colors possible being greenish-blue to black; it isfrui-ther-.indescent in thin xym; extremely fine grained; appearing to have a' cellular network which extends across 'scratches of the diamond point. It is Vpointed out that whilev the diamond point indents the 'sui-face, it 'does not remove the surface structure as described above. To demonstrate still further the magnitude of the surface hardnes of the present product, reference is made to the foliowingmaterials .75

for results ot scratch tests, performed under similar conditions as those already described:

Brass Sr-150; a Brinell hardness number= 5to 70 Monel metal S=320;

Brinell hardness number=ll to 300 Nickel S=380;

Brinelll hardness number: 90 to 300' relationship the apparent Brineli hardness number of the chromium carbide-surface of Fig. 3 ranges between 2000 and 4000. While we have 4described several methods of, and products resulting from, carburization of chromium and tungsten plated metallic bodies, it is to' be clearly understood that the present invention is in no way limited to the aforegoing 2.5 specific ingredients, temperatures and other quantities, but that the invention is rather to be construed in the light of thesfoliowing claims, since many other modiiications will readily occur to those skilled in the art from the present disclosure.

What we claim is: f,

l. As a new article of manufacture, a metallic body having a thin layer consisting only of chromium carbide on, and adhering to, avchromium plated surface of the body..

2. As a new article of manufacture, a metal body having only a superficial layer of tungsten carbide on, and adhering to. a tungsten plated surface of the body.

40 3. As a novel product, a-ferrous body,- a surface of. the body being plated with a layer of a single metal of the group including chromium and tungsten, the exposed surface of said layer being carburized.

4. As a novel product, a metallic body, a surface of the body being plated with a layer of a single metal of the group including chromium and tungsten, the exposed surface of said layer terial, of substantially less thickness than the bon oarbunzed, said surface being corburmed to a depth such that its surface hardness is of the vorder of four times that of the uncarburized plate surface. v

5. An article of1` manufacture consisting of a 6 metallic foundatiobodyea-ehromium plate deposit provided on the entire exposed face of said body, the metal of said body VNbeinother than the metals of the group including xchrbxnium, and a skin of surfacing material of substantially l0 less thickness than the thickness of the `pla dryness deposit on said plate which is extremely harder`wx than either the plate or said body, said material` "s 'in a uniform layer free from microscopic iis:

sures, the uniformity being unimpaired by sudden temperature variations. 7. An article of manufacture consisting of a metallic foundation bo'`y; a plate deposit, conslsting substantially of a metal of the group including chromium and tungsten, provided on a surface of the body; the composition of said body being free of said metal; a skin of surfacing mathickness of said plate deposit, on said plate; said material consisting substantially of the carbide of said metal.

8. As an article of manufacture, a metallic t foundation body, a surface of the body being 40 plated with a layer of a metal of the group including chromium and tungsten, the exposed surface of the said layer being a carbonaceous compound of said metal, and said surface being characterized by a coloration which is in marked con- 45 trast to that of the plated layer.

` CHARLES A. MARLIES.

GEORGE E. WHITE. 

